This invention relates to tufting machines and more particularly to the detection of broken yarn ends adjacent the needles of the machine and is an improvement of the detector disclosed in U.S. Pat. No. 4,522,139.
In a tufting machine more than 1,000 needles each carrying an individual yarn is employed for penetrating a backing material to insert loops of yarn therein, the loops being seized by a loop seizing looper or hook. Because of defects in the yarn itself or because of excessive tension or friction or other conditions, yarn breaks frequently occur before the yarn is stitched into the backing. When this occurs the product is defective and must be repaired as soon as the defect is detected. In some instances the defect goes undetected or is difficult to repair, especially when the gauge, i.e., the spacing between adjacent needles is fine or close, and the fabric produced is rendered defective which may require it to be discarded. Thus, it is highly desirable to detect a broken yarn end and stop the machine to repair the defect.
In the aforesaid patent assigned to the same assignee of the present invention, the prior art was discussed and a reliable broken yarn end detecting device was disclosed. That apparatus utilizes a multiplicity of yarn engaging fingers each having an eyelet for receiving a strand of yarn and being pivotably mounted in a support housing, the fingers normally being held in a raised position by the yarn, but dropped when the yarn passing through an eyelet of a finger is broken to provide a signal such as, for example, interruption of a light beam to activate a circuit for shutting power to the tufting machine motor to stop the machine.
Although the aforesaid apparatus is highly effective in operation, a number of maintenance and manufacturing problems result from the design thereof. For example, the fingers are supported in a housing through which a steel rod or shaft extends for pivotably mounting the fingers. Thus, a hole has to be drilled or bored through the housing for receiving the rod which supports the fingers which pivot relative to the rod within slots in the housing. Since it is difficult and expensive to drill a hole all the way through the housing, the housings are limited in length to approximately four inches thereby necessitating a substantial number of such housings to accommodate the need for a finger to correspond to each yarn end. Additionally, and of significance, is the fact that the fingers, which are formed from hardened steel, constantly pivot on the rod or shaft resulting in wear grooves being formed on the shaft. Eventually these rods or shafts wear out and must be replaced. Since the shaft extends all the way through the housing, and since the grooves in the shaft effect a distortion to the shaft, removal of the shaft from the housing is both difficult and time consuming. Furthermore, when a rod or shaft is removed from the block all of the fingers also are no longer held in the block. Thus, not only is it difficult to disassemble this apparatus, but it is also time consuming to reassemble all of the fingers associated with the rod or shaft. Another, and related, problem is that if one finger is bent or damaged so that it must be replaced the rod or shaft must be withdrawn completely because of the difficulty in attempting to merely remove it to the location of the